Method of heating a windshield to remove and prevent ice accumulations



I INVENTORS I HARRY R. KARP ALLEN w. BLANCH/1RD H. R. KARP El AL METHODOF HEATING A WINDSHIELD TO REMOVE FIG. 1

AND PREVENT ICE ACCUMULATIONS Original Filed June 17, 1949 April 2, 1957ATTORNEY United States Patent METHOD OF HEATING A WINDSI-HELD TO RE-MOVE AND PREVENT ICE ACCUMULATIONS Harry R. Karp, Hillside, and Allen W.Blanchard, Aliendale, N. J., assignors to Bendix Aviation Corporation,Teterboro, N. J., a corporation of Delaware Original application June17, 1949, Serial No. 99,764, now Patent No. 2,616,018, dated October 28,1952. and this application March 1, 1952, Serial No.

3 Claims. (Cl. 219-20) The present application is a division of U. S.application Serial No. 99,764, filed June 17, 1949, by Harry R. Karp andAllen W. Blanchard and now U. S. Patent No. 2,616,018, granted October28, 1952, and assigned to Bendix Aviation Corporation. The presentapplication relates to a novel method of applying heat to a transparentpanel and more particularly to a novel method for controlling theapplication of heat to the windshield of an aircraft to effect theremoval and prevention of the accumulation of ice thereon.

An object of the invention is to provide a novel method for controllingthe application of heat to the windshield of an aircraft so as to limitthe rate of change of temperature to a safe value so as to avoid thermalshock or other damage caused by a too rapid change of temperature whenthe temperature of the windshield is below a predetermined safe value,while providing a desirable and more rapid rate of temperature changewhen the temperature of the windshield is above the predeterminedcritical safe value. I

The above and other objects and features of the inven tion will appearmore fully hereinafter from a consideration of the following descriptiontaken in connection with the accompanying drawings wherein one structurefor carrying out the novel method of the invention is illust-rated byway of example. i

In the drawing:

Figure l is a schematic diagram of a control system for a heater of atransparent panel or windshield.

Figure 2 is a cross-sectional view of a solenoid operated clutch. I I Ip v r Figure 3 is a sectional view of the clutch of Figure 2 taken alongthe line 33 thereof.

Referring to the drawingof Figure 1, there is illustrated a controlsystem for a windshield heater claimed broadly in copending applicationSerial No. 68,594, filed December 31, 1948, by Joel D. Peterson andspecifically disclosed and claimed in the aforenoted parent applicationSerial No. 99,764, filed June 17, 1949, by Harry R. Karp and Allen W.Blanchard and now U. S. Patent No. 2,616,018, granted October 28, 1952,and assigned to Bendix Aviation Corporation. The control system includesan alternator 5 of suitable type and which may be driven by an aircraftengine as a source of power, and a variable transformer 7 which isarranged to modify the output voltage applied by the alternator 5 to aheater 9 of a windshield or transparent panel. g

The heater 9 of the windshield maybe transparent electrical conductivecoating applied to the windshield of a type such as sold under thetrade-names NESA and Electra-Pane. The heater 9 is connected byconductors 1 1 and 12 to the output of the transformer 7. The conductor12 is connected to a movable arm 13 of the transformer 7. Thetransformer 7 is connected by conductors 15 and 16 to the output of thealternator 5. The conductor 16 iscontrolled by on-oif switch 17 andlimit switch 19 connected in parallel.

windshield and comprises a resistance having a high tem peraturecoefficient, such as tungsten, and is used as a master to determine theamount and rate of application of heat to the windshield. Thetemperature element 21 may be of such a type as described and claimed incopending application Serial No. 151,009, filed March 21, 1950, by JoelD. Peterson as a division of the application Serial No. 68,594, filedDecember 31, 1948.

The temperature element 21 forms one arm of an alternating currentexcited bridge 22. A non-thermal sensitive reference resistor 23 servesasanother leg of the bridge 22, and the remaining legs are provided byWindings 24 and 25 forming the secondary of transformer 26. The bridgecircuit is supplied within alternating current by primary winding 27 ofthe transformer 26 inductively coupled to the secondary windings 24 and25. The winding 27 is connected to a suitable source of alternatingcurrent. The resistor 23 is of a value such as to balance the bridgewhen the control temperature, say for example, 120 F. is reached. Theoutput of the bridge will be directional or phased, depending uponwhether the resistance of the element 21 is above or below the referenceresistor 23 which is connected into the bridge by an onoff switch 28mechanically connected to switch 17. The output voltage of the bridge 22is connected by conductors 30 and 31 to the input of a phase-sensitivedetector and amplifier 32.

The output of the amplifier 32 is connected by conduct-ors 33 and 34 toone phase winding of a reversible motor 35, which may be of thetwo-phase type; and the other phase winding being connected byconductors 28A and 29A across the source of alternating current foroperation of the motor 35 in a manner well known in the art. The outputshaft 36 0f the motor 35 is mechanically connected to deliver torque toa gear train 37. The gear train 37 is ofthe two speed type having aratio changing system and solenoid control clutch for selecting outputspeeds of rotation of N or N/ 10, the operation of which will beexplained.

The output of the gear train 37 is mechanically connected by a shaft 38to rotate the movable arm 13 of the variable transformer 7 to provide anoutput voltage dependent upon the posit-ion of the movable arm. Theinput voltage of the transformer 7 will be the output voltage of.

the alternator 5. 7 'Thus, when the .value of resistor 21 is below thatof the resistor 23, the bridge 22 will be unbalanced in a direction toenergizethe reversible motor 35- so as to drive the movable arm 13 ofthe transformer. 7 in a direction toincrease the 'voltage applied to thewindshield 9. When the value of the resistor 21 is above that of theresistor 23, the bridge 22 will be unbalanced in the A temperaturesensing element 21 is embedded in the opposite direction to energize themotor 35 so as to drive the movable arm 13 of the transformer 7 in adirection to decrease the voltage applied to the windshield 9. Upon thevalues of the resistors 21 and 23 being equal the bridge will bebalanced, hence the motor 35 will not be energized and as long as thetemperature of the windshield remains constant, the voltage suppliedthereto will beconstant. As the temperature changes the control systemwill continuously adjust itself to maintain a constant preselectedtemperature at the windshield or transparent panel 9regardless ofchanges in outside air temperature or heat transfer conditions.

Novel method of windshield heater control In order to avoid thermalshock or other damage caused by a too rapid change in temperature, thenovel method herein described and claimed limits the rate of change to asafe value when the temperature of the windshield or transparent panel 9is below a predetermined value, say for example F. However, when thetemperature of the windshield 9 reaches the predetermined temperature, afast reaction to temperature changes due to changes in outside airtemperature, aircraft speed, and heat transfer conditions is desirableand is provided under the present method.

In the system disclosed herein, the method is carried out by means ofthe two-speed gear train 37 in which two operating speeds areautomatically obtained. The gear train 37 is mechanically connected tobe operated through a solenoid controlled clutch as will be explainedhereinafter with reference to Figures 2 and 3. Control for the solenoidis provided by an auxiliary circuit 41 connected by conductors 43 and 45across the output of the bridge 22. The auxiliary circuit 41 may, forexample, be an amplifier circuit so arranged as to have energy flowingin its output circuit when the temperature of the windshield 9 is belowa predetermined value of, for example, 100 F. A pilot relay winding 51is connected by conductors 47 and 49 across the output of the circuit41. The relay winding 51 controls an armature element 53 arranged toclose switch contacts 55 upon the winding 51 being energized. Closingthe switch contacts 55 energizes the solenoid of the two-speed clutch 37through condoctors 57 and 59 from a source of D. C. electrical energy60.

Upon energization, the solenoid actuates the clutch and thereby the geartrain 37 to its N gear ratio where it will be maintained as long as thecontrol solenoid is energized. When the gear train 37 is in thisposition, the movable arm 13 of the transformer 7 will be rotated slowlygiving a slow rate of temperature rise.

Upon the temperature of the windshield 9 reaching 100 F., the auxiliarycircuit 41 will cause relay winding 51 to release the armature 53 underspring tension and return the switch contacts 55 to an open positiondeenergizing the control solenoid of the gear train 37 and return thegear train 37 to its normal N/lO ratio. In this latter position themovable arm 13 will be rotated at a faster rate thus providing fastaction to give good response in the region of the control temperature.

The solenoid controlled clutch gear train 37 may be the clutch and geartrain assembly illustrated by Figures 2 and 3 and disclosed and claimedin application Serial No. 99,765, filed June 17, 1949, by Harry R. Karpand Philip J. Guillot and now U. S. Patent No. 2,616,019, grantedOctober 28, 1952, and assigned to Bendix Aviation Corporation.

Secured to the input shaft 36 of the gear train 37 is a sun gear 63which meshes with planet gears 65, which in turn mesh with orbit gear67. The input shaft 36 is rotatably supported in housing 69 by bearing71. Securely attached to the shaft 61 is a clutch plate 73. The planetgears 65 are supported on shafts 75 carried by spiders 77 and 78. Thespider 77 is splined to output shaft 38 which is rotatably supported inthe housing 69 by a bearing 72. A compress-ion spring 81 bears againstthe spider 77. Adjacent to the orbit gear 67 on the housing 69 is aclutch facing 83. A solenoid winding 85 is arranged around the innercircumference of the housing 69. The winding 85 is connected throughswitch 55 to the source of direct current 60 by the conductors 57 and59. The orbit gear 67 and spider 78 serve as the armature of thesolenoid.

In operation, when the solenoid winding 85 is deenergized as shown inFigure 2, the spider 78 is held in intimate contact with the clutchplate 73 by the pressure of the spring 81. This locks the planetarysystem and permits it to rotate with the shaft 36. When the solenoidwinding 85 is energized, the pressure of the spring 81 is overcome andthe spider 78 is moved out of contact with clutch plate 73 and the orbitgear 67 is biased by the solenoid 85 into intimate contact with theclutch facing 83, whereupon the shaft 38 is driven through the planetarygear system.

When the pilot determines that heat will be needed at the windshield 9,he may manually actuate the switch 17 '4 t to the on" position and closeswitch 28 in the bridge circuit 22 so as to place the bridge circuit 22in an operative condition sensitive to temperature changes. Theunbalance in the bridge circuit 23 causes the solenoid to actuate thegear train 37 to the N ratio. The movable arm 13 of the variabletransformer operated by shaft 38 begins to rotate slowly increasing thevoltage applied to the windshield 9. As the movable arm 13 moves awayfrom its low voltage position, the limit switch 19 operated by the arm13 automatically returns to its normally closed position.

When the temperature of the windshield 9 reaches F. the auxiliarycircuit 41 opens the switch 55 and the solenoid 85 becomes de-energized.Spring means 81 actuate the gear train 37 to its N/lO ratio so that thearm 13 driven by shaft 38 rotates faster until the temperature is F. Asthe temperature varies from 120 F., an unbalanced voltage appears at theoutput of the bridge 22 of such a phase as to cause the motor 35 todrive the arm 13 in such a direction as to increase (or decrease) theenergy supplied and thus maintain 120 F. at the windshield 9.

To shut off the system, the switch 17 is actuated to its off position.This also opens the interconnected switch 28 in the bridge circuit 22introducing a large unbalanced voltage in the system of such a phase asto cause motor 35 to drive the arm 13 to a low voltage position. Thisunbalanced voltage also causes the auxiliary circuit 41 to energize thesolenoid 51 and close switch 55 to energize solenoid 85 which actuatesthe gear train 37 to its N ratio thereby rota-ting the arm 13 at a slowrate, thus limiting the rate of decrease of temperature.

Upon the arm 13 reaching its minimum voltage position, it willautomatically operate the limit switch 19 to cut off all power to thesystem. The system will then be in the proper position when it isrecycled.

The automatic temperature control system limits the rate of change oftemperature to a safe value and also continuously adjusts itself tomaintain a constant preselected temperature at the windshield regardlessof changes in outside air temperature or heat transfer conditions. Theonly manual control required is the on-off switch 17-28, all othercontrols being automatic dependent upon conditions in the system.

Although only one structure for carrying out the novel method of thepresent invention has been illustrated and described, various otherstructures and changes in the form and relative arrangements of theparts of such structure may be made to carry out the novel method of thepresent invention.

What is claimed is:

l. A method for preventing accumulation of ice upon a surface of atransparent panel of an aircraft, comprising the steps first of applyingheat to such surface, second increasing the heat applied to such surfaceat a relatively slow rate so long as the temperature of the panel isbelow a predetermined range so as to prevent thermal shock, and thirdincreasing the heat applied to such surface at a more rapid rate uponthe panel temperature being within the predetermined range and until thetemperature of the panel reaches a predetermined value.

2. The method defined by claim 1 including the further step ofdecreasing the heat applied to such surface at said rapid rate upon thepanel temperature exceeding said predetermined value so as to regulatethe temperature of said panel to said predetermined value.

3. A method for preventing accumulation of ice upon a surface of atransparent panel of an aircraft exposed to ice forming conditions,comprising the steps first of sensing the temperature of said panel,second applying heat to such surface and increasing the heat applied tosuch surface at a relatively slow rate so long as the sensed paneltemperature is below a predetermined safe range so as to prevent damageto the transparent panel by thermal shock, third increasing the heatapplied to such surface at a more rapid rate upon the sensed paneltemperature being within the predetermined safe range and until thetemperature of the panel reaches a predetermined value, and fourthdecreasing the heat applied to such surface at said rapid rate upon thesensed panel temperature exceeding said predetermined value so as toregulate the temperature of said panel to said predetermined value.

1,942,587 Whitman Jan. 9, 1934 6 Stammberger Dec. 24, Goodwillie Dec.31, Hubbard Ian. 18, Guyer et a1. Nov. 20, Mershon Feb. 22, Mershon Nov.15, Mershon Nov. 21, Burton et a1. June 19, Mershon June 10, MershonAug. 26, Karp et a1. Oct. 28, Guillot et a1. Oct. 28,

